Today's featured chart looks at dew point climatology by wind direction for the month of August for Des Moines. While there is a clean signal shown for a dew point dependence on wind direction, the magnitude of the signal is not that large. Rewording, in Iowa humidity levels during the month of August are generally supported by our transpiring vegetation more so than air mass transport of humidity into the state. Certainly originating from our south and southwest will carry more moisture than that from our northwest, but drier air will also promote more transpiration when there is available soil water, so air mass modification will take place to wash out some of the difference. You can generate this chart for other months of the year and compare the magnitude of the changes.

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